LeetCode121. The best time to buy and sell stocks

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One 、 Ideas

Find the selection and status

Two 、 problem

Given an array prices , It's the first  i Elements  prices[i] Represents the number of shares in a given stock i Sky price .

You can only choose One day Buy this stock , And choose A different day in the future Sell the stock . Design an algorithm to calculate the maximum profit you can get .

Return the maximum profit you can make from the deal . If you can't make any profit , return 0 .

Example 1：

 Input ：[7,1,5,3,6,4]
 Output ：5
 explain ： In the  2  God （ Stock price  = 1） Buy when , In the  5  God （ Stock price  = 6） Sell when , Maximum profit  = 6-1 = 5 .
      Note that profit cannot be  7-1 = 6,  Because the selling price needs to be higher than the buying price ; meanwhile , You can't sell stocks before you buy them .

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Example 2：

 Input ：prices = [7,6,4,3,1]
 Output ：0
 explain ： under these circumstances ,  No deal is done ,  So the biggest profit is  0.

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Tips ：

• 1 <= prices.length <= 105
• 0 <= prices[i] <= 104

Related Topics

• Array
• Dynamic programming

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3、 ... and 、 Code

public int maxProfit(int[] prices) {

            if (prices.length < 2) {
                return 0;
            }

            int[][] arr = new int[prices.length][2];
            arr[0][1] = -prices[0];
            arr[0][0] = 0;

            for (int i = 1; i < prices.length; i++) {
                arr[i][0] = Math.max(arr[i - 1][1] + prices[i], arr[i - 1][0]);
                arr[i][1] = Math.max(- prices[i], arr[i - 1][1]);
            }
            return arr[prices.length-1][0];
        }

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